threshold_sub_pix (Operator)

Name

threshold_sub_pix — Extract level crossings from an image with subpixel accuracy.

Synopsis

threshold_sub_pix(Image : Border : Threshold : )

Description

threshold_sub_pix extracts the level crossings at the level Threshold of the input image Image with subpixel accuracy. The extracted level crossings are returned as XLD-contours in Border. In contrast to the operator threshold, threshold_sub_pix does not return regions, but the lines that separate regions with a gray value less than Threshold from regions with a gray value greater than Threshold.

For the extraction, the input image is regarded as a surface, in which the gray values are interpolated bilinearly between the centers of the individual pixels. Consistent with the surface thus defined, level crossing lines are extracted for each pixel and linked into topologically sound contours. This means that the level crossing contours are correctly split at junction points. If the image contains extended areas of constant gray value Threshold, only the border of such areas is returned as level crossings.

Parameters

Image (input_object)	singlechannelimage → object (byte / int1 / int2 / uint2 / int4 / real)
Input image.

Border (output_object)	xld_cont-array → object
Extracted level crossings.

Threshold (input_control)	number → (real / integer)
Threshold for the level crossings.
Default value: 128
Suggested values: 0.0, 10.0, 30.0, 64.0, 128.0, 200.0, 220.0, 255.0

Example

read_image(Image,'fabrik')
threshold_sub_pix(Image,Border,35)
disp_xld(Border,WindowHandle)

Result

threshold_sub_pix usually returns the value 2 (H_MSG_TRUE). If necessary, an exception is raised.

Parallelization Information

threshold_sub_pix is reentrant and processed without parallelization.

Alternatives

threshold

See also

zero_crossing_sub_pix

Module

2D Metrology